My immediate thought is that since you feel that EVERY system has underperformed, that it is most likely due to the room. Room acoustics can easily make or break the listening experience.
First off, try moving your speakers further out into the room and in different positions. I understand that the space competes with other uses, but you won't be the first to find out that the "prime" listening positions don't work with other room functions. That's OK. Just mark them and then move the speakers back to the wall when you're not doing serious listening. The same goes for other pieces of furniture, try moving them away from the listening area when you are doing your critical listening.
I think you will find that the room acoustics will have a much greater impact on the sound than the AC dedicated lines.
Just my 2cents.
Cheers,
Tom